The present invention relates to a fish sonar in which conditions underwater and the bottom of a lake or a pond are displayed by two pictures on a display for fishing for black bass.
Generally, in fishing for black bass as a sport, information of whether a region of the lake or pond has a soft or hard bottom is necessary because black bass inhabit the hard bottom portion. However, a fish sonar whether having one frequency or two frequencies mainly displays the conditions underwater in the lake or pond.
The reflectional strength of the ultrasonic waves is weak when ultrasonic waves are reflected by a soft bottom portion of a lake or pond. Therefore, it is difficult to receive the second and third reflectional waves of the ultrasonic waves from the soft bottom portions of the lake or pond. On the other hand, the reflectional strength of the ultrasonic waves is strong when the ultrasonic waves are reflected by a hard bottom portion of a lake or pond. Therefore, it is easy to receive the second and third reflectional waves of the ultrasonic waves from the hard bottom portions of the lake or pond.
However, even if it is desired that the second and third reflectional waves of the ultrasonic waves are received by the prior fish sonar providing two pictures using two frequencies and that the information on the condition of the bottom of the lake or pond is precisely obtained, when the depth range of this fish sonar is set to a deep condition, the picture between the position of the vibration in the water and the bottom in the lake or pond is compressed. It is difficult for the display of the fish sonar to display bottom conditions and fish underwater. Therefore, the bottom conditions and fish underwater in the lake or pond cannot be displayed by the prior fish sonar when the second and third reflectional waves of the ultrasonic waves are displayed by the fish sonar.